Railway track circuit



NOV. 8, 1938. I w PQWELL I 2,135,527

RAILWAY TRACK CIRCUIT Original Filed July 28, 1934 Compensafin Line BYATTORNEY Mum Patented Nov. 8, 1938 PATENT OFFICE RAILWAY TRACK CIRCUITWinfred T. Powell, Brighton, N. Y., assignor to General Railway SignalCompany, Rochester,

Original application July 28, 1934, Serial No. 737,433, now Patent No.2,083,920, dated June 15, 1937. Divided and this application December 3,1936, Serial No. 114,089

12 Claims.

This invention relates in general to track circuits such as used inrailway signalling practice and it has more particular reference tomeans for maintaining current through a track relay associated with astretch of railway track substantially constant, regardless of changesin ballast leakage between the rails of the track due to Weatherconditions.

The invention also relates to means for automatically discriminatingbetween current changes in the track circuit due to the occupiedcondition of the track and due to leakage currents resulting from poorballast conditions.

This application is a division of my prior application Ser. No. 737,433filed July 28, 1934, now

U. S. Letters Patent 2,083,920 dated June 15,

In railway operation it is quite essential that the usual track relayconnected across the track section at one end of a signalling block besufficiently energized when the block is unoccupied to pick up and holdup with certainty. It is likewise essential that the occupancy of thetrack section will so effectively shunt or condition the relay that itwill be positively released. For example, in the usual track circuits ifthe normal holding current is too high shunting may not be effective todrop the relay and if the normal holding current is so low that shuntingis made more positive then it is possible that at times the holdingcurrent will be insuflicient.

Taking the above into consideration it will be apparent that the usualvariation in ballast resistance encountered in practice, due primarilyto vchanges in weather conditions, may interfere with the properoperation of the track relay unless some means are provided tocompensate for the current ordinarily shunted away from the track relayby extreme ballast leakage, or for discriminating between changes due toballast resistance and track occupancy. The present arrangement isproposed as a means for regu lating the potential applied to the holdingwinding or windings of a track relay under various ballast conditionsand also for discriminating between slow changes in the shunting of therelay due to ballast changes and rapid changes in the shunting of therelay due to track occupancy.

It will be obvious that an increase in ballast resistance results .in adecrease in the leakage current between the rails so that the voltageacross the terminals of a track relay connected across these railsincreases. Conversely, as the ballast resistance-decreases the leakagecurrent between the rails increases and the terminal voltage at theusual track relay decreases. The relay current will vary over aconsiderable range and cover a range at times which may prevent properresponse of the relay under occupied or unoccupied conditions of thetrack section.

It is therefore proposed in accordance with this invention to providemeans automatically operable to permit a change in current in the trackrelay eifected by the entrance of a train into the associated tracksection, but to automatically maintain a substantially constant currentin the track relay regardless of changes in Values of leakage currentthrough the ballast from one rail to the other.

It is further proposed to improve the shunting eificiency of the trackcircuit and for this purpose a discriminating arrangement is included inthe circuit of the track relay which discriminates between a slow changein track shunt due to track ballast and a rapid change in track shuntdue to train occupancy.

Further objects, purposes and characteristic features of the inventionwill appear as the description progresses, reference being made to theaccompanying drawing which shows by way of example one form which theinvention may assume.

The single figure illustrates one form of the present invention in adiagrammatic and conventional manner.

Apparatus.---Referring to the single figure, a section of railway trackincluding rails I is shown separated from the adjacent track sections byinsulated joints 2. A track battery BT and a track relay T are shownconnected to the track rails at opposite ends of the illustratedsection.

As typical of the control exercised by the track relay, a semaphoresignal SG is illustrated at the left end of the track section and in thepresent description it will be assumed that traflic moves from left toright over this section as indicated by the arrow appearing above thetrack rails.

The track relay and the track rails are connected to the track batterythrough the medium of an electrical network comprising variousresistors, relays and impedance coils laid out in the form of aWheatstone bridge.

Normal conditions.-Referring to the drawing it will be assumed that theballast is in a dry condition so that there is approximately no leakagecurrent flowing between the rails l of the track section. Under thiscondition relay T is energized over a circuit extending from theterminal of battery BT, compensating line conductor l5, through thebridge network in the direction of the arrows, lower winding of relay Tand resistor H in multiple, compensating line wire i6, upper track rail,upper winding of relay T and lower track rail to the terminal of batteryET.

The Wheatstone bridge is made up of two resistors comprising arms a andb and two impedances comprising arms 0 and d, all having direct currentresistance values such that the product of arms ab equals the productofarms cd. Under this condition,'points A and B'of the bridge circuit areat equal potential so that no current flows through the upper winding ofdetector relay P.

Therefore track relay T' is energized by way of its potential windingwhich is connected across the track rails and also by way of its currentwinding which is connected in series with thebridge across thetrackrails. It will be understood that contact 33- of relay T is. usedto control the signals in any manner required by practical conditions.

Under these conditions relays P, G and AX are normally de-energized.

Track occupancy.-It will be assumed that a train enters the tracksection at the left end under the conditions above outlined, that is;normal dry ballast conditionsr The shunt provided across the track railsby the train, short circuits the upper winding of relay T. The lowerwinding of relay T is of such a value in ampere turns that the relaywill not hold up with current through the lower winding alone. Thereforethe shunting of the upper winding ordinarily drops the relay'forsignalling purposes.

In addition to this operation of relay T, a check is provided by thesudden shunting of the track by the train causing a sudden rushofcurrent from the terminal of battery BT, line I5, arm a of the bridge,upper winding of relay P, armb of the bridge,-resistor H, line l6, uppertrack rail, through the shunt provided by the train and thelower trackrail to the terminal of battery ET. This sudden increase of currentflows in the above described circuit in the direction of the arrows. Thereason that the current flows throughthe winding of relay P is becausethe bridge is out of balance under this condition due to arms 0 and dbeing inductive so that the sudden rush of current is choked out ofthese arms of thebridge; Therefore relay P will operate its'polarcontacts to the left. It will be understood that resistor H is providedin shunt-of the lower winding of relay T to provide a non-inductive pathfor thesudden rush of current which would ordinarily be choked back ifithad to go through the inductive winding of relay T.

The operation of relay P tothe left closes. a'

stick circuit for this relay and a pick-up circuit for therelay AXextending from contact 28 of relay P in its left hand dotted position,lower winding of relay P, contact 2| of relay P in its left hand dottedposition, back contact 22 of relay G- and" winding of relay AX, toRelayAX short circuits resistor H and the lower winding of relay T atits front contact 23-. Since both windings of relay T are noweffectively short ci'rcuited it will be positively released.

It will thus be seen that in the event of the failure of relay T torelease when shunted by a train an additional shunt is provided for positively releasing this relay in response to an impulse of current set upby the entrance of a train into the track section. In the event thatrelay T is dropped by the shunting of its upper winding alone then acircuit is closed for picking up relay AX extending from back contact 24of relay T, back contact 22 of relay G, and winding of relay AX, toUnder either of the above described conditions the dropping of backcontact 24 short circuits the lower winding of relay P which allows thisrelay to restore its contacts to neutral after a check has been madethat relay T has dropped. Relay P is not energiz'ed through its; upperwinding after the sudden rushof current because the bridge reaches astable condition, due to the direct current resistances of the arms ofthe bridge being so proportioned that no current flows between points Aand B'. 7

Track 1 .noccupancy.-When the train leaves the illustrated tracksection, a sudden decrease of current flow across the track rails iseffected. The removal ofthe shunt across the upper winding of relay Tis-eiiective to permit sufficient current toflow through this winding topick up re' lay T. Also this sudden decrease of current flow through thebridge causes a momentary rush of current in the opposite direction tothat indicated by the arrows which is efiective to operate relay P'tothe right. This rush of current is due tothe self-inductance ofinductances c and d which tends to maintain the original current flowafterthe current flow from battery BT has been decreased; The decreasedcurrent flow from the battery establishes an immediate value througharms a and b but there are momentary added currents in arms d and c inthe original direction (due to the self-inductance of these arms), whichcurrents are in aiding relation for causing a resultant current to flowthrough the upper winding. ofrelay? in'a' direction opposite to thearrow. This closes a circuit for sticking relay P and for pickingup'relayG extending from contact 21' of relay P in its right hand dottedposition, lower winding of relay P, contact 20' of relay Pinits righthand dotted position, front contact 25" of relay AX, to

The picking up of-relay G opens the circuit of relay AX at back contact22, allowing relay AX to drop its front contact 23 for removing theassumed that a high leakage current, due to an,

abnormally wet ballast condition, flows from the terminal: of batteryBT, line conductor i5, through the bridge, lower winding of relay T,line conductor l6; upper track rail, upper winding of relay T and thelower track rail to the terminal of battery BT. Due to the lowresistance ballast shunt, a substantial portion of v the current is"shunted from'the' upper winding of relay T. A'lsodue to this leakagecurrent an increase in current flow is effective through the' lowerwinding of relay T sothat the increased shunting eiTect of the upperwinding of the relay (due to' the leakage) will be compensated for bythe increased current flow through the lower winding of the relay due tothis leakage. It will be noted that any leakage current which flows mustgo through the lower winding of relay T.

Assuming that a train enters the track section and winding of relay G,

under this condition, the upper winding of relay T is short circuitedand the sudden shunting of the track by the train causes relay P toactuate its contacts to the left as before. This closes a circuit forpicking up relay AX and for sticking relay P'in its left hand position.This is assuming that relay T did not drop when the train shunted itsupper winding.

The picking up of relay AX short circuits the lower winding of relay Tand since its upper winding is shunted by the train, it will bepositively released. The dropping of relay T closes the above describedcircuit for relay AX which also short circuits the lower winding ofrelay P for restoring this relay to neutral.

When the train leaves the track section it will be assumed that, due tothe extremely high leakage current, relay T does not pick up because itsupper winding is eifectively shunted. Relay P, however, will actuate itscontacts to the right as previously described and a circuit closed forpickingup relay G extending from contact 2! of relay P in its right handdotted position, lower winding of relay P, contact of relay P in itsright hand dotted position, front contact of relay AX and winding ofrelay G, to It will be understood that relay AX is picked up because itis assumed that relay T is not picked up. It will be noticed that thisoperation of relay P sticks the relay in its right hand position bymeans of current flowing through its lower winding in opposition to thefull line arrow, which corresponds to the current which operated relay Pto the right which was opposite to the full line arrow in the upperwinding of relay P.

The picking up of relay G drops relay AX which inserts the lower windingof relay T in the track circuit and since the leakage current is high,suflicient current flows through this lower winding to positively pickup relay T. To prevent relay AX being again picked up before relay Tpicks up its back contact 24, relay G is made slightly slow acting.

The above rather specific description of one form of the presentinvention has been given solely by way of illustration and is notintended in any manner whatsoever in a limiting sense. It will beobvious that the general principles therein disclosed may be embodied inmany other organizations widely different from those illustrated withoutdeparting from the spirit of the invention defined in the followingclaims.

What I claim is:

1. Ina track circuit, a track relay, a source of current connected tothe railroad track, a potential winding and a current winding of saidrelay connected to said track, said potential winding being shunted by atrain on said track cir-' cuit, an electrical network connected to saidsource of current, means including said potential and said currentwindings for maintaining said relay eflectively energized under varioustrack leakage conditions, and means including said network responsive tosaid train shunt for shunting said current winding.

2. In a track circuit, a track relay, a source of current connected tothe railroad track, a potential winding and a current winding of saidrelay connected to said track, said potential winding being shunted by atrain on said track circuit, an electrical network connected to saidsource of current, means including said potential and said currentwindings for maintaining said relay 'efiectively energized under varioustrack leakage conditions, means including said network responsive tosaid train shunt for shunting said current winding, and means includingsaid network responsive to the removal of said train shunt for removingthe shunt from said current winding.

3. In a track circuit, an insulated section of track, a source ofcurrent connected to said track, a track relay including windingsconnected to said track and maintained picked up during the slowlychanging current values in its windings due to variations in ballastresistances, a Wheatstone bridge connected in series with said relay,means responsive to the entrance of a train into said section forproducing a rapid change in current in the circuit of said relay andsaid Wheatstone bridge whereby said bridge is unbalanced, and meanscontrolled in response to the unbalanced condition of said bridge andsaid train shunt for shunting one of said windings.

4. In a track circuit, an insulated section of track, a source ofcurrent connected to said track, a double wound track relay connected tosaid track and maintained picked up by an increase of current in onewinding when the current in the other winding decreases due to anincrease in ballast leakage current, the current in one of said windingsbeing decreased by the presence of a train on said track circuit, andmeans responsive to the entrance of a train into said section fordecreasing the current in the other winding whereby said relay isreleased.

5. In a track circuit; in combination with an insulated stretch oftrack; a source of current connected to one end and a track relayconnected to the other end of said track; and regulating meanscontrolled over said track by current from said source for automaticallyshunting at least a portion of said relay whereby the shunting efiect ofa train in said stretch of track is augmented, said regulating meansincluding a balanced detector which selectively detects current changesin said track due to its occupancy by a train and changes due to ballastleakage.

6. In a track circuit; in combination with an insulated stretch oftrack; a source of current connected to one end and a track relayconnected to the other end of said track; and regulating meanscontrolled over said track by current from said source for automaticallyshunting part of the winding of said relay whereby the shunting effectof a train in said stretch of track is augmented, said regulating meansincluding a balanced detector which selectively detects current changesof distinctive character in said track due to its occupancy andunoccupancy by a train and changes due to ballast leakage.

7. In a track circuit for railroads, the combination with a section oftrack insulated from the adjacent track by insulating joints, a sourceof track circuit current connected across the track rails at one end ofsaid section through the medium of a Wheatstone bridge consisting of twomultiple conductors each having an intermediate tap, said Wheatstonebridge having the four elements so formed constituting impedances havingelectrical constants so that said bridge is balanced and has no voltagebetween its taps for direct current flowing to said bridge but hasvoltage of one polarity impressed between said taps when the directcurrent through the bridge is increased and has voltage of oppositepolarity impressed between said taps when said direct current isdecreased, a polar relay connected between said taps, a second relay, acircuit for picking up said second relay when said polar relay isenergized to one polarity position, and a holding circuit for saidsecond relay which is broken when said polar relay is operated to theother polarity position.

8. In combination, a railway track divided into blocks by insulatingjoints, a signal at the entrance to each block, a track circuit for eachblock including a track battery and a Wheatstone bridge connected inseries, said Wheatstone bridge having four elements connected end to endto form a closed link of which two oppositely located elements are morehighly inductive than are the other two elements which bridge is soincluded in the track circuit that the track circuit current divides aportion flowing through two elements in series and the rest flowingthrough the other two elements in series said elements having ohmicresistances so that the bridge is balanced and no voltage exists betweenthe two points each joining two elements in series when direct currentflows therethrough but whereby voltage of one polarity exists betweensaid two points when the direct current is increased and Voltage of theopposite polarity exists between two points when the direct current isdecreased, a signal control relay for controlling the signal at theentrance to said block, and means including said Wheatstone bridge forpicking up said relay when voltage of one polarity exists between saidpoints and for dropping said relay when voltage of the opposite polarityexists between said points.

9. In combination, a railway track divided into blocks by insulatingjoints, a signal at the entrance to each block, a track circuit for eachblock including a track battery and a Wheatstone bridge connected inseries, said Wheatstone bridge having four elements connected end to endto form a closed link of which two oppositely located elements are morehighly inductive than are the other two elements and which bridge is soincluded in the track circuit that the track circuit current divides inflowing through said bridge a portion of the current flowing through twoelements in series and the rest of the current flowing through the othertwo elements in series said elements have ohmic resistances so that thebridge is balanced and no voltage exists between the two points eachjoining two elements in series when direct current flows therethroughbut whereby voltage of one polarity exists between said points when thedirect currentrsupplied by said battery is increased and voltage of theopposite polarity between said points exists when the direct currentsupplied by. said battery is decreasecl, a normally energized signalcontrol relay for controlling said signal which signal control relay iscaused to assume its deenergized position when said track circuit isinterrupted, means for causing said signal relay to assume itsdeenergized position when voltage of one polarity between said pointsexists and for causing said relay to assume its energized position whenvoltage of the opposite polarity exists between said points.

10. In a track circuit of the normally closed type, a section of trackinsulated from the rest of the track by insulating joints, a track relaynormally assuming an attracted condition and having two windingsarranged on the same core and having one winding connected across thetrack rails at one end of said section, a source of direct currentconnected across the track rails at the other end of said section, andmeans controlling the fiow of current in the other winding of said trackrelay to cause said track relay to assume its retracted condition uponsudden increase in the flow of current from said source to said trackcircuit and to assume its attracted condition in response to a suddendecrease in the flow of current from said source to said track circuit.

11. In a track circuit of the normally closed type, a section of trackinsulated from the rest of the track by insulating joints, a track relaynormally assuming an attracted condition and having two windingsarranged on the same core and having one winding connected across thetrack rails at one end of said section, a source of direct currentconnected across the track rails at the other end of said section, atwo-position relay controlling the flow of current in theother windingof said track relay to cause said track relay to assume itsretracted'condition when said to cause it to be actuated to one positionin response to a sudden increase in the flow of current from said sourceto said track circuit and to cause it to be actuated to its otherpositionin response to a sudden decrease in the flow of current fromsaid source to said track circuit.

12. In a track circuit of the normally closed type, a section of trackinsulatedfrom the rest of the track by insulating joints, a track relaynormally assuming an attracted condition and having two windingsarranged on the same core and having one winding connected across thetrack rails at one end of said section, a source of direct currentconnected across the track rails at the other end of said section, andmeans con: trolling the flow of current in the other winding of saidtrack relay including a neutral relay which is picked up in response toa sudden increase in the current supplied by said source to said trackcircuit and may be held up'through a holding circuit including a' backcontact of said track relay and including means for breaking saidholding circuit in response to a sudden decrease in the current suppliedto said track circuit by said source,

WINFRED T. POWELL,

